With the development of information and communication technology, a variety of wireless communication technologies are developed. Among them, a wireless LAN (wireless local area network, WLAN) is technology for allowing the Internet to be wirelessly accessed in home, a company, or a specific service providing region using a portable terminal such as a personal digital assistant (PDA), a laptop computer, or a portable multimedia player (PMP) based on radio frequency technology.
A standard for the wireless LAN technology is developed as an IEEE (Institute of Electrical and Electronics Engineers) 802.11 standard. IEEE 802.11a provides a maximum PHY data rate of 54 Mbps using a 5 GHz unlicensed band. IEEE 802.11b provides a maximum PHY data rate of 11 Mbps by applying a direct sequence spread spectrum (DSSS) at 2.4 GHz. IEEE 802.11g provides a maximum PHY data rate of 54 Mbps by applying orthogonal frequency division multiplexing (OFDM) at 2.4 GHz. IEEE 802.11n provides a PHY data rate of 300 Mbps for two spatial streams by applying multiple input multiple output-OFDM (MIMO-OFDM). IEEE 802.11n supports a channel bandwidth up to 40 MHz and, in this case, provides data rate of 600 Mbps.
As the spread of such a wireless LAN is activated and applications using the wireless LAN are diversified, the need of new wireless LAN technology for supporting a throughput higher than data rate supported by the IEEE 802.11n is increasing. Very high throughput (VHT) wireless LAN technology is one IEEE 802.11 wireless LAN technology proposed to support data rate of 1 Gbps or more. Above all, IEEE 802.11ac is developed as a standard for providing very high throughput in a 5 GHz band, and IEEE 802.11ad is developed as a standard for providing very high throughput in a 60 GHz band.
In a system based on such wireless LAN technology, a non-AP station operating in a power save mode (PSM) transmits a PS (power save)-poll frame to an access point for reception of data buffered in the access point. In this case, when a plurality of PS-poll frames are transmitted at the same time, a channel access competition among non-AP stations and collision among the PS-poll frames occur. Accordingly, since the non-AP station must be continuously kept in an awake state or repeatedly perform retransmission of a PS-poll frame not transmitted due to the collision until data is successfully received, a large amount of power is consumed.